Patellar Injuries

Patellar Injuries is a topic covered in the 5-Minute Emergency Consult.

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  • Usually caused by sudden flexion and external rotation of tibia on femur, with simultaneous contraction of quadriceps muscle
  • Direct trauma to patella is a less common cause
  • Lateral dislocation of the patella is most common, with the patella displaced over the lateral femoral condyle
  • Uncommon dislocations include superior, medial, and rare intra-articular dislocation

  • Direct trauma:
    • Most common mechanism
    • Direct blow or fall on patella
    • Usually results in comminuted or minimally displaced fracture, or open injury
  • Indirect forces:
    • The result of excessive tension through the extensor mechanism during deceleration from a fall (can also cause patellar tendon rupture)
    • Avulsion injury from sudden contraction of the quadriceps tendon
    • Usually results in transverse or displaced fracture (often both)
  • Types of patellar fractures:
    • Transverse: 50–80% (usually middle or lower 3rd of patella)
    • Comminuted (or stellate): 30–35%
    • Longitudinal: 25%
    • Osteochondral

Patellar Tendon Rupture
  • Usually caused by forceful eccentric contraction of quadriceps muscle on a flexed knee during deceleration (e.g., jump landing and weight lifting)
  • Often occurs in older athletes
    • Microtrauma from repetitive activity

Patellar Tendinitis
  • Overuse syndrome from repeated acceleration and deceleration (jumping, landing)


  • Risk factors for patellar dislocation:
    • Genu valgum (knock-knee)
    • Genu recurvatum (hyperextension of knee)
    • Shallow lateral femoral condyle
    • Deficient vastus medialis
    • Lateral insertion of patellar tendon
    • Shallow patellar groove
    • Patella alta (high-riding patella)
    • Deformed patella
    • Pes planus (flatfoot)
  • Common injury in adolescent athletes, especially girls
  • The younger the patient at the time of initial dislocation, the greater the risk of recurrence

  • Male:female ratio 2:1
  • Highest incidence in those 20–50 yr old

Patellar Tendon Rupture
  • Peak incidence in 3rd and 4th decades:
    • Often in athletes
  • Risk factors:
    • History of patellar tendinitis
    • History of diabetes mellitus, previous steroid injections, rheumatoid arthritis, gout, systemic lupus erythematosus
    • Previous major knee surgery

Patellar Tendinitis
  • Microtears of tendon matrix from overuse
  • Seen in high jumpers, volleyball and basketball players, runners

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